1. Technical Field
The present invention relates to a secondary battery and a battery module, and more particularly, to a battery module constructed by electrically connecting a plurality of unit batteries and a secondary battery used as a unit battery in the battery module.
2. Related Art
Recently, high-output secondary batteries using non-aqueous electrolytes of a high energy density have been developed. High-capacity secondary batteries are constructed by connecting a plurality of high-power secondary batteries in series so that they can be used for driving motors of, for example, electric vehicles or hybrid electric vehicles, which require high electric power.
Such high-capacity secondary batteries (‘battery modules’) are composed of a plurality of secondary batteries (‘unit batteries’) which are generally connected in series.
Each of the unit batteries includes an electrode group having a positive electrode, a negative electrode, and a separator interposed therebetween, a case having a space for accommodating the electrode group, a cap assembly combined with the case to seal the case, and positive and negative terminals protruding upward from the cap assembly and electrically connected to the positive electrode and the negative electrode, respectively, which are provided in the electrode group.
When prismatic batteries are used as the unit batteries, generally the prismatic batteries are arranged in a battery module such that positive and negative terminals of one unit battery alternate between positive and negative terminals of another unit battery adjacent thereto. Also, the positive terminals and the negative terminals of the adjacent unit batteries are connected to each other via conductors to form a battery module.
One battery module includes several or up to tens of unit batteries. Thus, because of the heat generated from these unit batteries, the volume of the battery module increases due to inclusion of a cooling structure for radiating heat generated from the respective unit batteries, a safety means, and a system circuit.
Further, a battery module having multiple unit batteries is equipped with an additional battery management system (‘BMS’), which limits an input or output current in order to prevent overcharge, over-discharge, over-current, excessive pressure, and overheating of the respective unit batteries.
However, in a conventional structure, the BMS has protective circuits for protecting the unit batteries during abnormal operation of the unit batteries together with circuits for controlling charging or discharging of the unit batteries so that a proper current can be applied to the unit batteries during charging or discharging thereof.
Therefore, the conventional BMS circuit structure can be complicated and difficult to design. In particular, in the case of battery modules that require high capacities for electric vehicles or hybrid electric vehicles, the number of unit batteries increases, necessitating simplification of the BMS.